Processing and Performance of Metal Fiber Reinforced High Temperature Superconductor
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PROCESSING AND PERFORMANCE OF METAL FIBER REINFORCED HIGH TEMPERATURE SUPERCONDUCTOR S. SALIB, C. VIPULANANDAN AND T. STONE Texas Center for Superconductivity, University of Houston, Houston, Texas 77204-5506. ABSTRACT Aggregation of YBa2Cu307-x powder by compaction molding and sintering results in porous ceramic with poor mechanical properties and hence improving the ceramic properties using continuous stainless steel fibers have been studied. Fiber reinforced beam specimens (2% of fibers by weight) were prepared by modifying the standard processing method. Fibers were pretreated with silver to reduce the contamination of the superconducting matrix. The mechanical and electrical properties of the superconducting ceramic-fiber composite was evaluated at 77K. Continuous stainless steel fibers improved the performance of the superconducting ceramic. INTRODUCTION The high temperature superconducting ceramic (HTSC) is brittle , as other ceramic materials and hence improving the ductility of the bulk material is considered a challenge. In order for the superconductor to be used widely or for its applications to be diversified, its strain to failure has to be improved. In the past ceramic materials have been reinforced using ceramic fibers such as alumina and silicon carbide. Singh and Gaddipati [1] used silicon carbide to improve the mechanical properties of mullite. The silicon carbide fibers were 140 gtm in diameter with the following properties: (1) elastic modulus of 400 GPa, (2) failure strain of 1.0% and (3) strength of 4.13 GPa. The composite was fabricated by uniaxially aligning the fibers and incorporating the mullite matrix around each fiber. The final consolidation of the matrix was done by hot pressing between 1500 0 C and 1700 0 C. Fiber loading of 25% by volume was used in the mullite-silicon carbide composite. The flexural strength was increased from 271 MPa for the monolithic to 780 MPa for the composite, and the strain to failure was increased from 0.18% for the monolithic to 0.98% for the composite. Mah et. al. [2] also used silicon carbide fibers to reinforce lithium aluminosilicate. They used silicon carbide fibers with a flexural strength of 2.07 GPa, elastic modulus of 193 GPa and failure strain of 1.1%. Fiber loading of 40% (by volume) was used. The flexural strength was increased from 172 MPa for the monolithic to 931 MPa for the composite, and the strain to failure increased from 0.2% for the monolithic to 0.9% for the composite. In recent times silicon carbide fibers have become very popular with ceramics. Use of metal fibers in ceramic matrix has been very limited. Studies have shown [3] that the use of steel fibers in cement type materials have the following benefits: (1) increases the tensile strength of the composite material, (2) eliminates brittle failure in tension if there is adequate bonding of fibers, (3) increases ductility and 4) improves crack control. Hence if steel type material can be effectively incorporated into HTSC, ductility can be improved and sudden mechanical and electri
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